1. Field of the Invention
The present invention relates generally to oil quality measurement and more specifically to systems and methods for single-sensor oil quality measurement.
2. Description of Related Art
When preparing food in a fryer, the quality of the cooking medium (e.g., the oil) may impact the quality of the food that is cooked by the fryer. As the cooking medium is used to cook food, particles of food may contaminate the cooking medium. The flavor characteristics of each of these food products may become infused to a greater or a lesser degree in the cooking medium. This infusion may adversely affect food quality. Moreover, upon heating the cooking medium, the cooking medium may undergo chemical reactions (e.g., hydrolysis, oxidation, and polymerization). These degradations may cause products such as free fatty acids, hydroperoxides, and polymerized triglycerides. Moreover, degradation may reduce the viscosity of the cooking oils, which also may decrease performance. In many instances, such degradation of the cooking medium does not become apparent to the human eye until a late stage of degradation. Thus, there is a need to measure the quality of the cooking medium, which directly correlates to its suitability for use in cooking.
One method of measuring the quality of cooking medium uses an electrode sensor immersed in the frying medium. The electrode is energized with an excitation voltage signal, and the resulting current flows from the energized electrode through the cooking medium to a ground. The measured value of this current corresponds to the cooking medium quality (e.g., the suitability of the cooking medium for use during cooking) Nevertheless, known electrode systems are not suitable for use in an open fryer. First, the construction materials must withstand cooking oil temperatures up to 450 degrees Fahrenheit (230 degrees Celsius). Second, the electrode must resist mechanical damage from cleaning and operator equipment abuse. Thus, the electrode must be sufficiently unaffected by contamination from suspended food particles, as well as from long-term varnishing by exposure to hot cooking medium.
In addition to the above problems, for use in a commercial fryer, known electrodes are not small enough to mount in the cooking vessel below the cooking medium level without interfering with the fry baskets or other mechanical features of the cooking vessel. Additionally, readouts from the electrodes must be sufficiently shielded such that they are sufficiently unaffected by the proximity of grounded metal objects in the cooking vessel (e.g., the fry baskets). Thus, the electrode must be small, but if the electrode is too small, then the electrode may not be capable of generating sufficient signal gain to generate an output signal of sufficient magnitude to resolve cooking medium quality differences with an adequate signal to noise ratio, Cooking media may have very high resistance, so the electrode current is very small, requiring a large circuit gain to create a usable signal.
Known electrodes use, for example, an interdigitated pattern of conductors deposited on a ceramic or a fiberglass substrate. These conductors have very small spacing. Such electrodes are too fragile for use in a commercial fryer. Additionally, such electrodes are too susceptible to contamination from food particles entering the small conductor spacing. Further, known electrodes, such as those described above, do not comply with food safety regulations.
Moreover, known systems for measurement of food cooking oil quality use, for example, a sensor in each vat of a fryer with multiple vats. In the known systems, the oil quality is monitored continuously. Further, in the known systems, the sensor is near the top of the vat but below a minimum level of oil required for proper operation of the known systems. This location reduces the risk of trapping contamination in the electrode gaps. In other known systems, each sensor is placed near the bottom of each vat, such that each sensor is fully immersed in the oil. In addition, in the known systems, the cooking media surrounding the sensor in each vat may be stationary or may engage in a negligible amount of motion related to convection, pressure, or other phenomena, such that the electrode is exposed to a static electric field and the current flow in the cooking media is steady. Further, the temperature of the cooking media at the electrode may be the desired cooking temperature and the measured conductivity does not have to be adjusted to compensate for a temperature difference.